However, many experts believe that such attacks were probably carried out by heterosexuals as a perverse form of 'gay-bashing'.
By raping someone they think is homosexual, the attackers are able to express both their hatred of gays and their sexual aggression, according to Gillian Mezey, a psychiatrist at St George's Hospital, south London, who specialises in treating both male and female rape victims.
Researchers believe, however, that most sex attacks on males occur within relationships or as 'date rapes', where the assailant is known by the victim. Here the rapist is likely to be gay.
Dr Mezey, co-author of Male Victims of Sexual Assault, believes that gang attacks are motivated by the desire to humiliate and dominate. She said that in some cases rapists have told victims they are being assaulted because they are gay. 'This type of rapist frequently has a history of violent anti-social behaviour and in a perverse way they want to prove their sexuality.'
She draws a comparison with rape in prison. 'There is a clear group of men who, although they lead a heterosexual life outside, regard themselves as very macho and see the aggressive act of penetrating another person as something manly.'
Harvey Milnes, a counsellor for Survivors, a support group for male victims of sexual attacks, agrees. 'I would think that 99 per cent of all rapes committed in public are perpetrated by heterosexual men. Imagine the power a man feels degrading and humiliating a woman or a child and think how much more power they would feel doing it to a man.'
The scale of the problem is still unknown. Welfare organisations believe that as many as nine in 10 attacks are not reported. In a study in 1989, only two out of 22 men who claimed to have been raped had gone to the police.
The Metropolitan Police investigated 30 offences of non-consensual buggery against adult males in the year to last April. Fear, humiliation and shock deter many men from reporting rape. Others believe they will be criminalised and heterosexuals will be branded as homosexuals.
The legal system also appears to act as a deterrent. Male rape does not exist as a criminal offence under British law; the assaults are recorded as non-consensual buggery. Convicted rapists can be imprisoned for life, whereas buggery carries a maximum sentence of 10 years. Men also run the risk of having their names published during court cases, unlike women, who are guaranteed anonymity.
The perception by some people of police officers as homophobic also plays a part in non- reporting. The Metropolitan Police has tried to alter this image by piloting a support unit for male rape victims. However, since it was opened in March it has dealt with only four cases.